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VCO-SSI2131

A basic and generic VCO based on SSI2131

VCO product image

Interface

Main panel

Name Type Description
coarse Potentiometer
fine Potentiometer
freq LED Bi-color LED Voltage value for tri, green for positive voltage, red for negative voltage
pulse width Potentiometer Almost full-range (0% ~ 100%) pulse width control of pulse
fm amt Potentiometer fm amount
pulse amt Potentiometer pwm amount
lfm Switch button FM type for fm, exponential (off) or linear (on)
lfm LED LED Blue LED indicates if lfm switched on
soft Switch button Sync type for sync, hard (off) or soft (on)
soft LED LED Blue LED indicates if soft switched on
lfo/osc Toggle switch Switch between oscillator mode and LFO mode

Fine-tuning

There are 3 rheostats on the PCB panel

Name Description
VR_SCALE Adjust frequency range (scale) for SSI2131
VR_HFT Adjust high frequency compensation for SSI2131's exponential converter
VR_SINE Adjust sine shaper in tri-to-sine circuit

Specification

Inputs

Name Type Vmin Vmax Description
v/oct Input 0V +10V
fm Input -5V +5V
sync Input -5V +5V Oscillator synchronization input, triggers on rising edge
pwm Input -5V +5V Pulse width modulation, only apply for pulse

Outputs

Name Type Vmin Vmax Description
sine Output -5V +5V Sine wave
tri Output -5V +5V Triangle wave
saw Output -5V +5V Downward sawtooth wave
pulse Output -5V +5V Pulse wave

Physical dimension

  • Height: 128.5mm (3U)
  • Width: 40.3mm (8hp)
  • Depth: 36mm

Power consumption

  • +12V: 38mA
  • -12V: 24mA
  • +5V: N/A

Miscellaneous

About soft sync

Soft sync synchronizes the SSI2131 to an external signal when the triangle waveform is falling and close to GND. A capacitively-coupled pulse on the SOFT SYNC input will cause the triangle to switch from falling to rising. If the voltage on TCAP is too high then synchronization will not take place. The synchronization is “soft” in that it only occurs within a narrow part of the oscillating cycle; at all other times it has no effect.

—— From SSI2131 datasheet, Page 6 - 7, SYNCHRONIZATION.

Design your panel

Blank panel design files in various file formats are provided. Drill holes are filled in black, soldering mask are filled in grey.

Available file formats:

Format Software / Toolchain
.afdesign Affinity Designer 2.6.5 (My main design tool)
.svg, .dxf Affinity Designer 2.6.5
.ai Adobe Illustrator 2022

Panel drills

FAREKIND VIRTUAL ASSETS, May 2025.